That's the battery vent tube that plugs into the neg side of the battery (upper top side you will see a small matching hole just match the hole to the plastic insert and push in) (point it down as gases vent into it and turn into a liquid were it is then stored to a point that simple removal and emptying keeps the battery acid from dripping down into the wires and engine compartment. Very important small piece thats needs to be put back to store battery acid.
The red cap is the positive side battery terminal protector snaps in two small holes on battery top to prevent accidental electrical contact.

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